diff --git a/js/src/common/utils/SubtreeRetainer.ts b/js/src/common/utils/SubtreeRetainer.ts
index 0d7be4baf..3024277a9 100644
--- a/js/src/common/utils/SubtreeRetainer.ts
+++ b/js/src/common/utils/SubtreeRetainer.ts
@@ -7,7 +7,7 @@ export default class SubtreeRetainer {
     }
 
     check(...callbacks: Function[]) {
-        this.callbacks.concat(...callbacks);
+        this.callbacks.push(...callbacks);
     }
 
     /**